1. Field of the Invention
The present invention relates to an image reader for correcting a specific pixel.
2. Description of Related Art
As an image reader for reading a medium having two-dimensional information typified by a copying machine, the so-called line sensor is used in general. The line sensor, having a plurality of photoelectric conversion elements (photodetectors) in the read width direction (main scanning direction), has the number of pixels and pixel density which are determined in accordance with the read width, optical resolution or the performance of an optical system (imaging system) combined. As typical examples of line sensors, there are CCDs (Charge Coupled Devices) and photodiode arrays using CMOS process. Since they are all semiconductor devices, defectives can occur at a certain rate because of the influence of foreign substances during a manufacturing process. In the image reader that acquires a two-dimensional image with a line sensor by moving an object to be read, the defectives due to foreign substances and the like can cause line images not included in the original image. Accordingly, in addition to the technique of reducing the percent defective in the semiconductor manufacturing process, a technique for correcting pixel defects has been investigated as well.
For example, Japanese Patent Laid-Open No. 10-308901/1998 discloses in FIG. 2 (see Patent Document 1) a defect detecting correcting circuit which causes an address detecting circuit 24 to identify the address of a defective pixel within a screen from a defect signal extracted by a detector 22; stores the address data in an address storage circuit 25; generates, according to the address data provided from the address storage circuit 25, a defect correcting pulse at the timing the defective pixel is output, and interpolates pixel signals of neighboring pixels into the defective pixel.
Japanese Patent Laid-Open No. 2004-356933 discloses in Paragraph [0018] (see Patent Document 2) image processing which estimates pixel data of a missing pixel in photodetectors arranged in a line from pixel data of a plurality of photodetectors on both sides of the missing pixel, and outputs an image closer to the original document image.
Patent Document 1: Japanese Patent Laid-Open No. 10-308901/1998 (FIG. 2).
Patent Document 2: Japanese Patent Laid-Open No. 2004-356933 (Paragraph 0018).